Here's another flashback to the sixties, with a description of just when radical campus opinion turned against Israel. It was thirty-five years ago, when Jews showed that they were no longer willing to play the left's designated role of victim, in the Six-Day War.

At that point, with the aggressor Arabs soundly and surprisingly trounced by the previous underdogs, the sympathy shifted to them, and a whole generation of reporters were unleashed on the world with that flawed paradigm.

There are two other reasons -

1) The US was backing Israel, and in 1967 it was fashionable to oppose the US on any and every issue

2) Jews are just no longer ethnic enough.

As someone who was a college student in 1967, I can assure you that the campus leftists were on the side of the Arabs long before the shooting started - Egypt, then called the UAR, was led by a leftist favorite, Gamal Abdul Nasser, who had nationalized industry, banks, etc. a dozen years earlier. And Nasser was a friend of the Soviets, thus a good man to all leftists.
I don't know that we can put an exact date on the leftist support of the Arab side.

I'm not sure where everyone concludes that the Israelis were supported by the US in 1967.

If we look at the make-up of the Israeli arsenal at that time, we find that most of the equipment was French. Their tanks were, for the most part, AMX-13s, some Centurions (British), and old Shermans, upgraded w/ new guns.

The main part of the Israeli flight-line were Mysteres (note that, at that time, our allies were flying F-104s and some F-4 Phantoms).

By 1973, the situation had changed, but that was long after the '67 War (which, indeed, had something to do w/ changing our policies).

Indeed, once it was demonstrably clear that the Soviets were interested in waging the same kind of war by proxy in the Middle East they were conducting in SE Asia, with a real prize in the oil to boot, the path became open for us to take a stand.

Especially when it became clear that it wasn't just Jews who had a problem with Arab behavior and that this could become a major issue in the next election.

We don't always get there for the right reasons but the important thing is that we got there.